What different types of holoprosencephaly exist?
Alobar, semi-lobar and lobar subtypes.
What is the key issue resulting in holoprosencephaly?
The fundamental problem is a failure of the developing brain to divide into left and right halves. This normally occurs early in the first trimester of pregnancy, at the end of the 5th week of gestation. Several factors have been implicated, including alcohol.
- monoventricle with partially developed occipital and temporal horns, but no frontal horns
- incomplete falx cerebri
- incompletely formed interhemispheric fissure, especially anteriorly
- highly dysplastic corpus callosum